The world is not hungry, but it is thirsty.1） It seems strange that nearly3/4 of the earth is covered with water while we say we are short of water.  Why? Because about 97% of water on the earth is sea water which we can't drink or use for watering plants directly. Man can only drink and use 3%—the water that comes from rivers and lakes. 2）而且由于有一些水已经被污染, 我们甚至不能全部利用。

    Now more water is needed. The problem is: Can we avoid（避免）a serious water shortage later on? Firstly, we should all learn how to save water. Secondly, we should find out ways to reuse it. Scientists have always been making studies in the field. 3） Today. in most large cities. water is used only once and then runs to the sea or rivers. But it can be used again. 4） Even if every large city reused its water. still it would not be enough. Thirdly, there is a lot of water in the sea. What we should do is to separate the salt from the sea water. This is expensive, but it's already used in many parts of the world.5）科学家们正在尽力找出一个更加便宜的方式来做这件事。So you see, if we can find a way out. we'll be in no danger of drying up.